Communication apparatus and communication method

ABSTRACT

This invention provides a communication apparatus and a communication method of transmitting and receiving command data for controlling a device connected to a communication line by selecting an arbitrary one of a plurality of different communication systems, wherein at least some of a plurality of command data of each of the different communication systems are used in all of the communication systems.  
     This invention provides a communication apparatus and a communication method of transmitting and receiving command data for controlling a device connected to a communication line by selecting an arbitrary one of a plurality of different communication systems and, on the basis of the received command data, generating control data for a device connected to the communication line, wherein at least some of a plurality of command data generated by each of the different communication systems are used in all of the communication systems.  
     This invention provides a communication apparatus and a communication method including a first communication mode which performs data communication on a first communication line on the basis of a first communication system, and a second mode which performs data communication on a second communication line on the basis of a second communication system different from the first communication system, wherein the communication modes are switched in accordance with a connection state with respect to the first communication line for the first communication system.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a communication apparatusprovided in an electronic device capable of transmitting and receivinginformation data via a digital interface, and a communication method ofthe apparatus.

[0003] 2. Related Background Art

[0004] Recently, apparatuses and systems for processing not only textinformation such as documents but also various information such asimages and sounds are beginning to be extensively used with theimprovement of the processing capability of a central processing unit(CPU) using a computer or the like, the progress of a graphicaloperating system (OS) for operating hardware, the increase in capacityand the progress of digitization of communication information in anetwork, and the development of information compression techniques.

[0005] With the development of such multimedia technologies, it isbecoming possible to transmit all types of data in all forms by allcommunication protocols via a single digital interface (digital I/F). Itis also becoming possible for an apparatus corresponding to onecommunication protocol and incorporating a plurality of units toexternally control each unit and exchange information with externaldevices.

[0006] As an example of the digital I/F bus systems described above, acommunication system has been proposed in which AV devices, such as adigital video tape recorder (to be referred to as a VTR hereinafter), adigital television receiver, and a tuner, and a personal computer (to bereferred to as a PC hereinafter) are mutually connected by an IEEE1394serial bus (to be referred to as 1394 hereinafter), and digital videosignals and digital audio signals are transmitted and received betweenthese electronic devices. An outline of this 1394 system will bedescribed below.

[0007] As shown in FIG. 1, the 1394 system includes, as digital devices,a PC and a VTR corresponding to VGA (Video Graphics Array) inputs from adigital I/F, and a digital camera (to be referred to as a DCAMhereinafter) and a digital cam coder (to be referred to as DVCR)corresponding to VGA outputs from a digital I/F. The DVCR and the PC,the PC and the VTR, and the VTR and the DCAM are connected by the 1394serial bus described above.

[0008] Each digital device described above has a function of relayingdigital data and control data on the 1394 serial bus. Also, a cable forthe 1394 serial bus includes three shielded twisted pair lines. Eachtwisted pair line is used to transfer protocol signals and data andsupply electric power. Therefore, the whole system can operate even whena certain device is turned off in the system.

[0009] The basic configuration of each digital device has an operationunit as a user interface, a display unit, a CPU for controlling theoperation of the whole device, forming packets for communication, andholding addresses, a digital I/F for the 1394 serial bus, and a switchunit for performing switching between a deck unit, a tuner unit, or acamera unit (neither is shown) and the digital I/F.

[0010] In this 1394 system, as shown in FIG. 2, communication isperformed at a predetermined communication cycle (125 μs). Data having atime axis such as video data or audio data is transmitted by isochronous(synchronous) communication by which a transfer band is guaranteed at afixed data rate. Control data such as a control command is transmittedirregularly, where necessary, by asynchronous communication.

[0011] In communication like this, a cycle start packet exists at thebeginning of each communication cycle, and a period for transmitting apacket for isochronous communication is set subsequently to the cyclestart packet. A plurality of channels of isochronous communication canbe simultaneously performed by assigning channel numbers to packets forisochronous communication.

[0012] For example, when channel 1 is assigned to communication from theDVCR to the VTR, the DVCR transmits an isochronous communication packetof channel number 1 onto the bus immediately after the cycle startpacket. Meanwhile, the VTR monitors packets on the bus and receives thepacket assigned with channel number 1. In this manner isochronouscommunication is executed between the DVCR and the VTR.

[0013] Analogously, when channel number 2 is assigned to a packet fromthe DCAM to the PC, isochronous communication is executed between theDCAM and the PC by transmitting the packet of channel number 2 onto thebus after the packet of channel number 1, and the isochronouscommunications between channel 1 and channel 2 are performed parallel. Aperiod from the completion of transmission of all isochronouscommunication packets in each communication cycle to the next cyclestart packet is used in asynchronous communication.

[0014] Bus management by which the 1394 serial bus system describedabove can operate will be described below.

[0015] An apparatus serving as a bus manager previously checks thenetwork structure and the connection states of all nodes and controlsbus communication by defining each node ID and controlling isochronouscommunication.

[0016] That is, in the communication system as described above, when thepower supply is turned on or when a new digital device is connected or acertain device is disconnected, node IDs (physical addresses #0, #1, #2,and #3 in FIG. 3) are automatically assigned to the individual devices(nodes) in accordance with their connection states by the followingprocedure based on an address program and an address table stored in aninternal memory of the CPU, thereby automatically setting topology.

[0017] This node ID assignment procedure will be briefly describedbelow. This procedure includes determination of the hierarchicalstructure of the system and assignment of physical addresses to thenodes.

[0018] Assume that the above digital devices, i.e., the PC, DVCR, VTR,and DCAM are nodes A, B, C, and D, respectively.

[0019] First, each node transmits to a partner node, to which this nodeis connected by the 1394 serial bus, information indicating that thepartner is its parent. While giving priority to a node firsttransmitting this information to its partner, the parent-childrelationship between the nodes in this system, i.e., the hierarchicalstructure of the system and a route node which is not a child of anyother node are finally determined.

[0020] More specifically, the node D informs the node C that the partneris a parent, and the node B informs the node A that the partner is aparent. If the node A informs the node C that the partner is a parentand the node C informs the node A that the partner is a parent, a nodewhich first transmits the information to its partner is given priority.That is, if the transmission from the node C is earlier, the node A isregarded as a parent of the node C. As a consequence, the node A is nota child of any other node. If this is the case, the node A is a routenode.

[0021] After the parent-child relationship between the digital devicesis thus determined, assignment of physical addresses is performed. Thisphysical address assignment is basically done in such a manner thatparent nodes permit child nodes to perform address assignment and thesechild nodes permit themselves to perform address assignment from oneconnected to the smaller port number.

[0022] When the parent-child relationship is determined as above in theexample shown in FIG. 3, the node A first permits the node B to performaddress assignment. As a consequence, the node B assigns physicaladdress #0 to itself. The node B sends this information onto the bus toinform the other nodes that “physical address #0 is already assigned”.

[0023] Next, the node A permits the node C to perform addressassignment, and the node C similarly permits the node D, i.e., the childof the node C, to perform address assignment. Consequently, the node Dassigns physical address #1, next to physical address #0, to itself, andsends this information onto the bus.

[0024] Thereafter, the node C assigns physical address #2 to itself andsends this information onto the bus. Finally, the node A assignsphysical address #3 to itself and sends this information onto the bus.

[0025] A data transfer procedure will be described next.

[0026] Data transfer is enabled by assigning physical addresses asdescribed above. In the 1394 serial bus system, however, arbitration ofthe bus use rights is performed by the route node prior to datatransfer. That is, in the 1394 as shown in FIG. 4, only data of onechannel is transferred at a certain timing. Therefore, the bus userights must be arbitrated first.

[0027] When each node wants to perform data transfer, the node requestsits parent node to issue the bus use right. As a consequence, the routenode arbitrates the requests for the bus use rights from these nodes. Anode which acquires the bus use right as a result of the arbitrationdesignates the transmission rate before beginning data transfer. Thatis, the node informs the transmission destination node that thetransmission rate is 100, 200, or 400 Mbps.

[0028] Thereafter, in the case of isochronous communication, thetransmission source node starts data transfer by the designated channelimmediately after receiving a cycle start packet transmitted by theroute node as a cycle master in synchronism with the communicationcycle. Note that the cycle master transmits the cycle start packet ontothe bus and also matches the time of the individual nodes.

[0029] In the case of asynchronous communication in which control datasuch as a command is transferred, on the other hand, after synchronoustransfer in each communication cycle is complete, arbitration forasynchronous communication is performed, and data transfer from thetransmission source node and the transmission destination node isstarted.

[0030] In addition to the IEEE1394 standard described above, the RS-232Cstandard and the RS-422 standard presently exist and are used as theconventional serial data communication methods. These standards assumemutual connection using serial binary data exchange between a dataterminal equipment (DTE) and a data circuit-terminating equipment (DCE).These standards are formed and open to the public by the AmericanNational Standards Institute (ANSI).

[0031] As another example of the digital I/F bus systems, a universalserial bus (to be referred to as a USB hereinafter) as defined inUniversal Serial Bus Specification (Revision 1.0, Jan. 15, 1996) isproposed. This bus is invented as an external bus for connecting a PCand its peripheral devices. An outline of this USB system will bedescribed below.

[0032] The connection form of the USB will be described with referenceto FIG. 3. This USB system comprises a host computer 300 such as a PC, aroute hub 302, a first device 304 which is a recording medium such as ahard disk, a composite device 306 such as a camera-integrated VTR, afirst hub 308, a second device 310 such as a video camera, a thirddevice 312 such as a VTR, a second hub 314, a fourth device 316 which isan input device such as a keyboard, and a fifth device 318 which is apointing device such as a mouse. A hub has a function of adding a USBdevice. Also, a device is a terminal equipment including a USB businterface (not shown). In this USB as shown in FIG. 3, the terminalequipments are connected via the hubs including the route hub 302 on thehost computer 300, thereby forming a multiple star connection.

[0033] Since the host computer 300 has rights to access the first,second, third, and fourth devices 304, 310, 312, and 316, data exchangebetween these devices is performed via the host computer 300. Therefore,bus arbitration between the devices is not performed.

[0034] In the USB, data transfer is performed by a frame whose unit is1±0.05 ms. FIG. 4 shows the structure of the frame in the USB. Packetsare packed in this frame in accordance with the purpose and transferred.Four types of packets are defined in the USB. The first one is a tokenpacket, the second one is a start-of-frame packet (to be referred to asan SOF packet hereinafter), the third one is a data packet, and thefourth one is a handshake packet. The frame is started by the SOFpacket.

[0035] The host computer 300 performs data transfer with a plurality ofdevices by sequentially sending data transfer requests previouslyscheduled in the frame. If data is large-amount data, such as imagedata, which cannot be contained in a single frame, the host computer 300divides the data in units of frames and transfers the divided data.

[0036] Packet fields are packed in the above four types of packets inaccordance with the purpose and transferred. In the USB, six types ofpacket fields are defined. The first one is an 8-bit packet identifierfield (to be referred to as a PID hereinafter), the second one is a7-bit address field (to be referred to as an ADDR hereinafter), thethird one is a 4-bit endpoint field (to be referred to as an ENDPhereinafter), the fourth one is an 11-bit frame number field, the fifthone is a 1- to 1023-byte data field, and the sixth one is a 5- or 16-bitcyclic redundancy checks field (the 5- and 16-bit ones will be referredto as a CRC5 and a CRC16, respectively, hereinafter). The four types ofpackets described above are constituted by combining these packetfields.

[0037]FIGS. 5A to 5D show the arrangements of the four types of packets.As shown in FIG. 5A, the token packet is constituted by the combinationof the PID, ADDR, ENDP, and CRC5 fields. As shown in FIG. 5B, the SOFpacket is constituted by the combination of the PID, frame number, andCRC5 fields. As shown in FIG. 5C, the data packet is constituted by thecombination of the PID, data, and CRC16 fields. As described above, thedata field has 1- to 1023-byte data. Also, as shown in FIG. 5D, thehandshake packet is constituted only by the PID.

[0038] In the USB, two transfer modes are defined. One is a full-speedtransfer mode whose average bit rate is 12 Mbps. The other is alow-speed transfer mode whose average bit rate is 1.5 Mbps.

[0039] Also, four data transfer methods are defined in the USB. Thefirst one is isochronous transfer. In isochronous transfer, a transferwidth which is a data amount of transfer performed for each frame and atransfer time from transfer request to transfer start are guaranteed.Also, in isochronous transfer, no retransmission request can be madeeven if an error occurs in transfer data. The second one is interrupttransfer. In interrupt transfer, only inputs from the individual devicesto the host computer 300 are possible. Also, in interrupt transfer, thedata transfer priority order on the bus is comparatively high. The thirdone is bulk transfer. In bulk transfer, the data transfer priority orderis the lowest of the four transfer methods. The fourth one is controltransfer. Control transfer is performed to exchange setup data forsetting up the individual devices.

[0040] The 1394 serial bus system and the USB described above arecommunication systems which have not been put into practical use untilrecently, and the conventional communication systems using RS-232C andRS-422 are still extensively used presently.

[0041] The present situation, therefore, is that all of digital devicescorresponding to the 1394, digital devices corresponding to the USB, anddigital devices corresponding to RS-232C and RS-422 coexist.

[0042] Accordingly, it is expected that apparatuses including theinterfaces of both the 1394 and the USB which are main streams in recentyears will be extensively demanded. It is also expected that apparatusesincluding both the 1394 interface and the interface of RS-232C or RS-422will be extensively demanded. Furthermore, it is expected thatapparatuses including a plurality of interfaces of, e.g., the 1394, theUSB, and RS-232C will be extensively demanded.

[0043] If, however, two or more types of communication devices areincorporated into a single apparatus to perform communication by two ormore communication systems, the circuit scale is increased, and thissignificantly increases the cost.

SUMMARY OF THE INVENTION

[0044] The present invention has been made in consideration of the abovesituation, and has as its first object to provide a communicationapparatus and a communication method capable of selecting two or morecommunication systems by using a single device without increasing thecost due to an increase in the circuit scale or deteriorating theoperability in setting device connection.

[0045] To achieve the above object, according to one preferredembodiment of the present invention, there are provided a communicationapparatus and a communication method of transmitting and receivingcommand data for controlling a device connected to a communication lineby selecting an arbitrary one of a plurality of different communicationsystems, wherein at least some of a plurality of command data of each ofthe different communication systems are used in all of the communicationsystems.

[0046] According to another preferred embodiment of the presentinvention, there are provided a communication apparatus and acommunication method of transmitting and receiving command data forcontrolling a device connected to a communication line by selecting anarbitrary one of a plurality of different communication systems and, onthe basis of the received command data, generating control data for adevice connected to the communication line, wherein at least some of aplurality of command data generated by each of the differentcommunication systems are used in all of the communication systems.

[0047] According to still another preferred embodiment of the presentinvention, there are provided a communication apparatus and acommunication method comprising a first communication mode whichperforms data communication on a first communication line on the basisof a first communication system, and a second mode which performs datacommunication on a second communication line on the basis of a secondcommunication system different from the first communication system,wherein the communication modes are switched in accordance with aconnection state with respect to the first communication line for thefirst communication system.

[0048] Other objects, features and advantages of the invention willbecome apparent from the following detailed description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0049]FIG. 1 is a view showing the connection form of an IEEE1394 serialbus;

[0050]FIG. 2 is a timing chart showing a communication example using theIEEE1394 serial bus;

[0051]FIG. 3 is a view showing the connection form of a USB;

[0052]FIG. 4 is a view showing a data transfer unit of the USB;

[0053]FIGS. 5A, 5B, 5C and 5D are views showing packets used in datatransfer of the USB;

[0054]FIG. 6 is a block diagram showing the arrangement of a digitalvideo camera of the first embodiment according to the present invention;

[0055]FIGS. 7A and 7B are views showing general formats of command datafor the IEEE1394;

[0056]FIG. 8 is a flow chart showing the flow of digital I/F switchingcontrol according to the present invention;

[0057]FIG. 9 is a block diagram showing the arrangement of a videocamera of the second embodiment according to the present invention;

[0058]FIGS. 10A and 10B are views showing data formats transmitted froma host in bulk transfer;

[0059]FIG. 11 is a view showing ACK returned from an SD video camera ofthis embodiment in bulk transfer;

[0060]FIG. 12 is a view showing the arrangement of a data packet in thisembodiment; and

[0061]FIG. 13 is a block diagram showing the arrangement of a digitalvideo camera using the data packet shown in FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0062] The first embodiment of the present invention will be describedbelow with reference to the accompanying drawings. FIG. 6 is a blockdiagram showing the embodiment in which the present invention is appliedto a video camera, i.e., a so-called SD (Standard Definition) videocamera, for recording and reproducing an SD video signal.

[0063] Referring to FIG. 6, this SD video camera comprises a lens 1, animage sensing device 3 such as a CCD, a camera processing unit 5, arecording medium 7 such as a magnetic tape, a helical scan head (to bereferred to as a head hereinafter) 9, an error correction circuit (to bereferred to as an ECC hereinafter) 11, a video signal processing circuit13, a switch circuit 15, an audio signal processing circuit 17, and asubcode data processing circuit 19.

[0064] The SD video camera further comprises an auxiliary dataprocessing circuit (to be referred to as an AUX data processing circuithereinafter) 21, an arithmetic processing unit (to be referred to as anMPU hereinafter) 23, a format circuit 25, an interface circuit (to bereferred to as an I/F circuit hereinafter) 27, a read-only memory (to bereferred to as a ROM hereinafter) 29, a 1394 driver 31, an RS-232Cdriver 33, a 1394 I/O port 35, an RS-232C I/O port 37, a servo circuit39, a data bus 41, and a mode controller 43.

[0065] An object image taken through the lens 1 is photoelectricallyconverted by the CCD 3 and subjected to predetermined signal processingby the camera processing unit 5. Consequently, a luminance signal Y andcolor difference signals V and U are generated at a ratio of 4:1:1 asdigital video signals. These digital video signals thus generated areinput to the switch circuit 15.

[0066] In performing encoding, the digital video signals are appliedfrom the switch circuit 15 to the video signal processing circuit 13under the switching control by the MPU 23. The video signal processingcircuit 13 performs compression coding for the 4:1:1 digital videosignals by block formation, discrete cosine transform (to be referred toas DCT hereinafter), quantization, and fixed-length coding.

[0067] Also, in performing encoding, a digital audio signal is inputfrom a circuit (not shown) such as a microphone or an audio amplifier tothe audio signal processing circuit 17 via the switch circuit 15 andencoded by the audio signal processing circuit 17. Additionally, subcodedata and AUX data are input from the MPU 23 to the subcode dataprocessing circuit 19 and the AUX data processing circuit 21,respectively, and processed by these circuits.

[0068] The video signal, audio signal, subcode data, and AUX dataprocessed by the video signal processing circuit 13, the audio signalprocessing circuit 17, the subcode data processing circuit 19, and theAUX data processing circuit 21, respectively, are input to the ECC 11through the data bus 41. The ECC 11 adds an error correcting code tothese signals. The signals are then transmitted through a modulationcircuit and a head amplifier (neither is shown) and written on themagnetic tape 7 with the head 9.

[0069] In performing decoding, on the other hand, the head 9 reproducesdigital signals from a track on the magnetic tape 7. The ECC 11 performserror correction for the reproduced digital signals. Of the digitalsignals output as digital block data from the ECC 11 to the data bus 41,the video signal processing circuit 13 connected to the data bus 41decodes a video signal to generate a luminance signal Y and colordifference signals U and V at a ratio of 4:1:1. These generated signalsare output outside via the switch circuit 15.

[0070] Of the digital signals output as digital block data from the ECC11, an audio signal is input, similar to the video signal, to the audiosignal processing circuit 17 through the data bus 41. The audio signalis decoded by the audio signal processing circuit 17 and output outsidevia the switch circuit 15. Meanwhile, the subcode data processingcircuit 19 and the AUX data processing circuit 21 connected to the databus 41 input decoded subcode data and AUX data, respectively, to the MPU23.

[0071] The compression-coded video and audio data are input to theformat circuit 25 through the data bus 41. While the video signalprocessing circuit 13 and the audio signal processing circuit 17 areperforming encoding, the input video and audio data to the formatcircuit 25 are data before the error correcting code is added by the ECC11. On the other hand, while the video signal processing circuit 13 andthe audio signal processing circuit 17 are performing decoding, theinput video and audio data to the format circuit 25 are data after theerror correcting code is removed by the ECC 11.

[0072] The output subcode data and AUX data from the MPU 23 are alsoinput to the format circuit 25. The format circuit 25 reconstructs thesevideo data, audio data, subcode data, and AUX data into DIF data(digital interface data) and outputs these DIF data to the I/F circuit27. These DIF data are packeted by the I/F circuit 27.

[0073] Note that the format circuit 25 and the I/F circuit 27 are socontrolled by the MPU 23 as to perform processing suited to the selectedone of the 1394 interface and the RS-232C interface.

[0074] When the 1394 interface is to be used, the packet data formed bythe I/F circuit 27 is supplied to the 1394 I/O port 35 via the 1394driver 31. When the RS-232C interface is to be used, the packet dataformed by the I/F circuit 27 is supplied to the RS-232C I/O port 37 viathe RS-232C driver 33.

[0075] The 1394 driver 31 monitors the state of connection to the 1394serial bus by detecting the power supply voltage of a power supplytwisted pair line of 1394 twisted pair lines, and outputs dataindicating the connection state (to be referred to as 1394 connectionstate data hereinafter) to the MPU 23. The power supply voltage level ofthe power supply twisted pair line is raised when the 1394 serial bus isconnected to the 1394 driver 31, and is lowered when the bus isdisconnected. Therefore, the connection state can be detected bymonitoring this voltage level.

[0076] The 1394 interface and the RS-232C interface can also be switchedby the user by operating an external select switch (not shown) orautomatically switched by, e.g., the MPU 23 by detecting the connectionsof the interfaces.

[0077] Although the automatic switching between the interfaces will bedescribed later, the mode controller 43 switches the communication modes(switches the communication systems IEEE1394 and RS-232C) in accordancewith a setting signal (to be described later) sent from the MPU 23.

[0078] The servo circuit 39 controls the running of the magnetic tape 7in accordance with a designation signal from the MPU 23. Note that theMPU 23 performs processing in accordance with input designatinginformation from an operation panel (not shown) and manages theoperation mode of the whole system of this digital VTR and its variousstatus transitions.

[0079] This servo circuit 39 primarily has a function of stationarilymaintaining the driving of a rotary drum and a capstan (neither isshown). That is, the servo circuit 39 is connected to a capstan motor(not shown) for controlling the tape feed speed, a capstan FG (FrequencyGenerator) for checking the rotating state of the capstan motor, a drummotor for rotating a rotary drum, and detectors FG and PG (PhaseGenerator) for checking the rotational speed and the rotational phase ofthe drum motor. These components are controlled by the servo circuit 39.

[0080] Command data for the SD video camera of this embodiment isexternally applied to the 1394 I/O port 35. FIGS. 7A and 7B are viewsshowing general formats of the 1394 command data applied to the 1394 I/Oport 35. Referring to FIGS. 7A and 7B, CT and RC are 4-bit codesindicating a command type and a response code, respectively. Table 1below shows codes of the command type, and Table 2 below shows codes ofthe response code. TABLE 1 CT/RC code (binary) MSB LSB Command type 0 00 0 Control command 0 0 0 1 State inquiry command 0 0 1 0 Supportinquiry command 0 0 1 1 Report request command 0 1 0 0 (Unused) 0 1 0 1(Unused) 0 1 1 0 (Unused) 0 1 1 1 (Unused)

[0081] TABLE 2 CT/RC code (binary) MSB LSB Response code 1 0 0 0Conditions unfulfilled 1 0 0 1 Admitted 1 0 1 0 Rejected 1 0 1 1Transiting 1 1 0 0 Conditions fulfilled/standby 1 1 0 1 Already changed1 1 1 0 (Unused) 1 1 1 1 Busy

[0082] Referring to FIGS. 7A and 7B, HA indicates a header address, andEHA indicates an extended header The header address is an 8-bit code andused as an identification code for a plurality of subdevices in onedevice connected to a communication interface (communication line). Thatis, the five upper bits of the header address indicate a subdevice typerepresenting the type of the subdevice, and the three lower bits of theheader address indicate a subdevice number representing the number ofthe subdevice among subdevices of the same type indicated by the fiveupper bits. The extended header address is a header address reserved forthe future. Table 3 below shows examples of the subdevice type. TABLE 3Code (binary) MSB LSB Subdevice type 0 0 0 0 0 Video monitor 0 0 0 0 1(Unused) 0 0 0 1 0 (Unused) 0 0 0 1 1 (Unused) 0 0 1 0 0 Video cassetterecorder (VCR) 0 0 1 0 1 TV tuner 0 0 1 1 0 (Unused) 0 0 1 1 1 Videocamera 0 1 0 0 0 (Unused) . . . 1 1 1 1 1

[0083] Referring to FIGS. 7A and 7B, OPC indicates an operation code,and OPR indicates an operand. The operation code indicates the contentsof control with respect to a digital device connected to a communicationinterface (communication line). The operand indicates data required bythe operation code. Table 4 below shows examples of the operation codeand operand for reproduction. TABLE 4 OPC OPR Reproduction 0xC3 Nextframe 0x30 Lowest rate 0x31 Low rate 4 0x32 Low rate 3 0x33 Low rate 20x34 Low rate 1 0x35 Normal rate (x1) 0x36 High rate 1 0x37 High rate 20x35 High rate 3 0x38 High rate 4 0x39 Highest rate 0x3A Preceding frame0x3B

[0084] The unit of the data length of a command shown in FIGS. 7A and 7Bis four bytes. If the data length does not reach an integer multiple offour bytes, data in which all bits are zero is packed in the end of abit stream so that the data length is an integral multiple of four bytesas a whole.

[0085] When the user intends to cause the video cassette recorder (VCR)to perform normal reproduction in the case where the 1394 command datashown in FIGS. 7A and 7B are represented as shown in Tables 1 to 4, acode of command data such as “0x0021C336” (0x indicates hexadecimalnotation) is input from an external device. That is, the first “0x00”indicates four bits fixed to 0 at the beginning of the command data andsubsequent four bits (see Table 1) representing that the command data isa control command. The next “0x21” indicates an 8-bit header address andshows that the subdevice type is a VCR (see Table 3) and the subdeviceis the second device in the VCR. The next “0xC336” indicates anoperation code and an operand obtained from Table 4.

[0086] When this code for normal reproduction is input to the 1394 I/Oport 35, on the basis of this input code the I/F circuit 27 generates anaddress in the ROM 29 storing control data for normal reproduction andapplies the address to the MPU 23. In accordance with the generatedaddress, the MPU 23 reads out the control data from the ROM 29 andcontrols the rotary drum and the capstan motor (neither is shown) viathe servo circuit 39, thereby holding the reproduction state.

[0087] Meanwhile, command data for RS-232C is externally input to theRS-232C I/O port 37. In this embodiment, at least some command data ofthe 1394 command data and the RS-232C command data are used in the bothsystems.

[0088] For example, command data received by the 1394 driver 31 and theRS-232C driver 33 by their respective communication systems and havingthe same function are used in the two systems. More specifically, assumethat M (=integer of 2 or more) command data are transmitted and receivedby RS-232C and N (=integer of 2 or more, N≧M) command data includingcommand data having the same functions as the M command data aretransmitted and received by the 1394. If this is the case, all of the Mcommand data are used in both the 1394 and RS-232C. Alternatively, someof the M command data are used in the two systems.

[0089] With this arrangement, a communication device including the I/Fcircuit 27, the MPU 23, and the like which perform various controloperations by interpreting command data can be shared by the 1394communication system and the RS-232C communication system. Thiseliminates the need to provide a plurality of communication devices forvarious communication systems in one digital device. Accordingly, adigital device corresponding to both the 1394 and RS-232C communicationsystems can be manufactured without increasing the circuit scale.

[0090] In RS-232C, two digital devices are usually connected in aone-to-one correspondence with each other. This makes deviceidentification codes, device numbers, and the like data unnecessary. Inthis embodiment, therefore, a code such as “0xC336” is input to theRS-232C I/O port 37 to indicate the same normal reproduction. Table 5below shows examples of the RS-232C reproduction codes corresponding tothe 1394 control codes described above. TABLE 5 Reproduction code Nextframe 0xC330 Lowest rate 0xC331 Low rate 4 0xC332 Low rate 3 0xC333 Lowrate 2 0xC334 Low rate 1 0xC335 Normal rate (x1) 0xC336 High rate 10xC337 High rate 2 0xC335 High rate 3 0xC338 High rate 4 0xC339 Highestrate 0xC33A Preceding frame 0xC33B

[0091] When data is transferred by omitting the identification code andthe device number of a device as described above, a delay time caused bycommand transfer can be reduced. This is convenient when RS-232C whichis a relatively-low-rate interface is used.

[0092] When this code for normal reproduction is input to the RS-232CI/O port 37, on the basis of this input code the I/F circuit 27generates an address in the ROM 29 storing control data for normalreproduction and inputs the address to the MPU 23. In accordance withthe generated address, the MPU 23 reads out the control data from theROM 29 and controls the rotary drum and the capstan motor (neither isshown) via the servo circuit 39, thereby holding the reproduction state.

[0093] In the above embodiment, the command data applied to the 1394 I/Oport 35 and the RS-232C I/O port 37 and having the same function are thesame in the two communication systems. However, even when these commanddata are different, an increase in the circuit scale can be prevented bygenerating common control data in the two communication systems from theROM 29 on the basis of the command data.

[0094] If this is the case, the I/F circuit 27 and the MPU 23 generatethe same control data for command data received by the 1394 I/O port 35and the RS-232C I/O port 37 by their respective communication systemsand having the same function. That is, the I/F circuit 27 whichgenerates addresses in the ROM 29 storing control data corresponding tothe command data received by the I/O ports 35 and 37 generates the sameaddress in the ROM 29 for the command data received by the twocommunication systems and having the same function.

[0095] The above embodiment is described by using the IEEE1394 standardand the RS-232C standard. However, some other standard (e.g., the RS-422standard) can also be used. Also, when common command data is used fornot only a communication apparatus corresponding to two communicationstandards but also a communication apparatus corresponding to a largernumber of communication standards, the communication apparatus can bemanufactured without increasing the circuit scale.

[0096] In the above embodiment, the two lower bytes of the controlcommand are the same in the IEEE1394 standard and the RS-232C standard.However, this common part can have another arrangement. Additionally,the code length for control is not limited to the above-mentioned codelength (four bytes), so any arbitrary code length can be applied.

[0097] In this embodiment as described above, in an apparatus in which agiven one of a plurality of different communication systems is selectedto transmit and receive command data for controlling devices connectedto a communication line, at least some of a plurality of command data ofthe different communication systems or of a plurality of device controldata generated on the basis of the received command data are used in allof these communication systems. Therefore, a common communicationapparatus for performing various control operations by interpreting thecommand data or the control data can be used in the differentcommunication systems. That is, it is unnecessary to provide a pluralityof communication apparatuses for the different communication systems inone device. Consequently, it is possible to provide a communicationapparatus which can select two or more different communication systemsand does not largely increase the cost due to an increase in the circuitscale.

[0098] The automatic interface switching will be described below.

[0099] As described above, the 1394 driver 31 inputs the 1394 connectionstate data to the MPU 23 in addition to the control data from the 1394serial bus. If data indicating that the 1394 serial bus is connected isinput, the MPU 23 supplies a 1394 setting signal to the mode controller43 in order to set the communication mode in the 1394 mode. Uponreceiving the 1394 setting signal, the mode controller 43 holds the 1394driver 31 active and holds the RS-232C driver 33 in sleep.

[0100] On the other hand, if the 1394 driver 31 is disconnected from the1394 serial bus, the power supply voltage of the power supply twistedpair line of the 1394 twisted pair lines drops. The 1394 driver 31detects this voltage drop and outputs to the MPU 23 data indicating thatthe 1394 driver 31 is disconnected from the 1394 serial bus. Uponreceiving this 1394 connection state data, the MPU 23 supplies anRS-232C setting signal to the mode controller 43 in order to set thecommunication mode in the RS-232C mode. When this RS-232C setting signalis input, the mode controller 43 sets the 1394 driver 31 in sleep andthe RS-232C driver 33 active.

[0101]FIG. 8 is a flow chart showing the flow of interface switchingcontrol. Referring to FIG. 8, the control is started from step 0. Instep 1, the communication mode is reset to the 1394 mode. In step 2, the1394 driver 31 is set active. In step 3, the RS-232C driver 33 is set insleep.

[0102] In step 4, the level of the power supply voltage of the powersupply twisted pair line of the 1394 twisted pair lines is compared witha threshold voltage Th previously determined in the system to checkwhether the power supply voltage is higher than the threshold voltageTh. This threshold voltage Th is set to, e.g., 4 V.

[0103] If the power supply voltage of the power supply twisted pair lineof the 1394 twisted pair lines is higher than the threshold voltage Th,the flow returns to step 2. If this is the case, the processes in steps2 to 4 form a loop to hold the 1394 driver 31 active and the RS-232Cdriver 33 in sleep.

[0104] On the other hand, if it is determined in step 4 that the powersupply voltage of the power supply twisted pair line of the 1394 twistedpair lines is lower than the threshold voltage Th, the flow advances tostep 5. In step 5, the 1394 driver 31 is set in sleep. In step 6, theRS-232C driver 33 is set active. In step 7, the communication mode isset in the RS-232C mode. In final step 8, the control is completed.

[0105] Although not shown in the flow chart of FIG. 8, in thisembodiment the power supply voltage of the power supply twisted pairline of the 1394 twisted pair lines is measured at fixed time intervals.If this measured power supply voltage is higher than the thresholdvoltage Th previously set in the system, the control start routine instep 0 is started. Therefore, even after the communication mode is setin the RS-232C mode, if the 1394 driver 31 is again connected to the1394 serial bus, the communication mode is automatically switched to the1394 mode.

[0106] In this embodiment as described above, it is unnecessary toprovide a plurality of communication apparatuses for variouscommunication systems in one digital device. Therefore, a digital devicecorresponding to two communication systems of the 1394 and RS-232C canbe manufactured without increasing the circuit scale.

[0107] In this embodiment, data communication is performed in the 1394communication mode when the 1394 driver 31 is connected to the 1394serial bus. When the 1394 serial bus is disconnected, the RS-232C driver33 is automatically activated to perform data communication in theRS-232C communication mode. Therefore, even when a plurality of devicesare connected to both the 1394 serial bus and the RS-232C data channel,no connection setting operation need be performed, and high operabilitycan be realized.

[0108] Although the above embodiment is described by using the IEEE1394standard and the RS-232C standard, another standard (e.g., the RS-422standard) can also be used in place of the RS-232C standard.Alternatively, a communication line of any other standard than theIEEE1394 standard can be used, provided that the channel has a functionof supplying power.

[0109] The second embodiment according to the present invention will bedescribed below with reference to the accompanying drawings. FIG. 9 is ablock diagram showing the embodiment in which the present invention isapplied to a video camera, i.e., a so-called SD (Standard Definition)camera, for recording and reproducing an SD video signal. The secondembodiment differs from the first embodiment in that the firstembodiment includes the IEEE1394 and RS-232C as digital interfaces, butthe second embodiment includes the IEEE1394 and the USB. That is, thisembodiment discloses an apparatus in which at least some of command dataor of a plurality of device control data generated on the basis of thereceived command data are used in communication systems of both the 1394and the USB. The same reference numerals as in FIG. 6 denote the sameparts in FIG. 9, and a detailed description thereof will be omitted.

[0110] Referring to FIG. 9, this apparatus comprises a bit inversioncircuit 45, a USB driver 47, and a USB I/O port 49.

[0111] Video and audio DIF data are directly input from a data bus 41 toa format circuit 251. The format circuit 25′ also receives subcode dataand AUX data from an MPU 23, converts the data into DIF data, andoutputs the DIF data. This DIF data is packeted by an I/F circuit 27′.

[0112] The format circuit 25′ and the I/F circuit 27′ are so controlledas to perform processing suited to one of the 1394 interface and the USBinterface selected by the MPU 23.

[0113] When the 1394 interface is to be used, data is supplied to a 1394I/O port 35 via a 1394 driver 31. When the USB interface is to be used,data is supplied to the bit inversion circuit 45, the USB driver 47, andthe USB I/O port 49.

[0114] The 1394 and the USB transmit data by using different bit outputmethods; i.e., the most significant bit is transmitted first (MSB first)in the 1394, and the least significant bit is output first (LSB first)in the USB. When the USB is used, therefore, the bit inversion circuit45 performs bit inversion for data to be transmitted and received. Inthis embodiment, bit inversion is performed for data to be transmittedand received by the USB on the basis of the 1394. However, bit inversioncan also be performed for data to be transmitted and received by the1394 on the basis of the USB.

[0115] The 1394 interface and the USB interface can be switched by theuser by using an external select switch or can also be automaticallyswitched by detecting the connections of these interfaces.

[0116] The automatic interface switching will be described later.

[0117] As shown in the first embodiment, a code such as “0x0021C336” isinput from an external device when the user intends to cause a VCR toperform normal reproduction.

[0118] When this normal reproduction code is input from the 1394 I/Oport 35, on the basis of the input code the I/F circuit 27′ generates anaddress in a ROM 29 storing data for normal reproduction and applies theaddress to the MPU 23. In accordance with this address data, the MPU 23reads out the control data from the ROM 29 and controls a rotary drumand a capstan motor (neither is shown) via a servo circuit 39, therebyholding the reproduction state.

[0119] On the other hand, when the user intends to perform normalreproduction in the same manner as above by using the USB, a code istransmitted from a host (not shown) by the bulk transfer describedearlier. In the bulk transfer, a token packet as shown in FIG. 10A istransmitted in the start frame of the bulk transfer. In the next frame,the host transmits a data packet as shown in FIG. 10B. A code such as0x0021C336 described above is contained in a data field of this datapacket. Transmission of such comparatively small data is complete by twoframes because data up to 1,023 bytes can be contained in the datafield. TABLE 6 PIDs of token packet PID name PID value OUT 11100001₂ IN01101001₂ SETUP 00101101₂

[0120] TABLE 7 PIDs of data packet PID name PID value DATA0 11000011₂DATA1 01001011₂

[0121] The PIDs in the token packet will be described below. The firstPID is OUT indicating that data transfer from the host is started, thesecond PID is IN indicating that data transfer to the host is started,and the third PID is SETUP indicating that device setup is started.Table 6 above shows the values of these PIDs. Note that all tokenpackets are issued by the host.

[0122] A data packet has two kinds of PIDs. If the data packet is notcomplete in one frame, the first frame is started from DATA0, and PIDsare toggled like DATA0/DATA1/DATA0/ . . . in units of frames. Table 7above shows the values of these PIDs. In this embodiment, only one frameof the data packet is transmitted. Therefore, only DATA0 is used as thePID value.

[0123] As described above, the USB and the 1394 have different bitoutput methods. In the USB, therefore, a code such as 0x0021C336 in the1394 described above arrives at the USB driver 47 in the form of a codesuch as 0x0084C3CA formed by performing bit inversion in units of bytes.Accordingly, the bit inversion circuit: 45 converts a code having thevalue 0x0084C3CA into a code having the value 0x0021C336 by performingbit inversion in units of bytes, and outputs the converted code. In thisembodiment, the bit inversion circuit 45 is provided separately from theUSB driver 47. However, the USB driver 47 can also have this function.

[0124] When the transmission from the host is complete, the SD videocamera of this embodiment informs the host of the completion of thetransmission by using a handshake packet as shown in FIG. 11. Thishandshake packet is constituted only by PID and changes the meaning ofinformation in accordance with the value of the PID. Table 8 below showsthe values of the PID. ACK indicates that the communication is normallycomplete. NACK indicates that the data from the host has an error. Ifthis is the case, the host repeats the same data transfer as above.STALL indicates that the SD video camera of this embodiment is madeunable to perform data transmission/reception for some reason. TABLE 8PIDs of handshake packet PID name PID value ACK 11010010₂ NACK 01011010₂STALL 00011110₂

[0125] When informed by ACK that the communication is normallycompleted, the host again transmits the token packet to the SD videocamera of this embodiment in order to receive a response code. In thenext frame, the SD video camera of this embodiment inserts, e.g., aresponse code 0x0921C336, indicating that normal reproduction ispossible, into a data packet and transmits the data packet. Whennormally receiving the data packet, the host transmits the ACK handshakepacket to the SD video camera of this embodiment to complete onetransmission/reception.

[0126] In this embodiment, the control code and the response code areexchanged by using only bulk transfer. However, USB interrupt transfercan also be used in transmitting the response code. This configurationhas the advantage that the response code can be reliably returned evenif the data amount on the communication line is increased, sinceinterrupt transfer has a higher transfer priority order than that ofbulk transfer. Also, isochronous transfer can be used instead of bulktransfer in exchanging the control code and the response code.

[0127] USB communication can also be performed by adding additionalinformation to a data packet for performing the communication. FIG. 12shows a whole data packet when the additional information is added, andthe arrangement of a data field in the data packet. This data packet istransmitted by, e.g., isochronous transfer. During the transmission, thedata field of the data packet is transmitted by a fixed length from thestart to the end of the communication.

[0128] In the data field shown in FIG. 12, a field to be transmittedfirst is a data_length field. The data length of the data_length fieldis set to, e.g., 1 byte. This field indicates an effective data lengthcontained in the data field in units of bytes. A fixed_length_data_fieldfollows the data_length field. This field is a fixed-length data fieldas described above. This field includes a valid_data field containingeffective data to be actually decoded and a zero_pad_byte field in whichdata whose value is 0 is packed. If the data length of the valid_datafield equals the data length of the fixed_length_data_field, thezero_pad_byte field does not exist in the fixed length data field. Thevalue of the zero_pad_byte field is not limited to zero, and some otherdata such as 0xFF can also be used. The data length of thefixed_length_data_field is set to, e.g., 15 bytes.

[0129] In the data field shown in FIG. 12, an RS code field to betransmitted last is an error detecting-correcting code such as aReed-Solomon code. Although a Reed-Solomon code is used in thisembodiment, another error detecting-correcting code such as a Hummingcode can also be used. In this embodiment, a Reed-Solomon code having,e.g., 8 bytes is added.

[0130]FIG. 13 is a block diagram in which a communication apparatususing the data packet shown in FIG. 12 is applied to an SD video camera.The same reference numerals as in FIG. 9 denote the same parts in FIG.13, and a detailed description thereof will be omitted. Referring toFIG. 13, this SD video camera comprises a second error correctingcircuit (ECC) 51 and a second data bus 53.

[0131] When normal reproduction is to be performed, a code in which thevalue of the valid_data field in the data field shown in FIG. 12 is0x0021C336 is applied from an external device to the USB driver 47 viathe USB I/O port 49. Since the effective data length is set to fourbytes, the value of the data_length field is 0x04. In fact, the value ofthe above data is bit-inverted in units of bytes. The bit inversioncircuit 45 converts this bit-inverted value into a normal value. Eachconverted data is supplied to the second error correcting circuit 51through the second data bus 53, and errors occurring on thecommunication line are detected and corrected. In this embodiment,4-byte correction is possible.

[0132] With the above arrangement, even in isochronous transfer in whicha retransmission request cannot be made by NACK, the accuracy of data incommunication can be increased. Also, the use of isochronous transferhaving a comparatively high priority order has the advantage that theresponse can be rapidly performed in exchanging data. Note that the dataformat described above can contain not only the data length and theerror detecting correcting code but also some other additionalinformation. Note also that the numbers of bytes of the data_lengthfield, the fixed_length_data_field, and the RS_code field are notlimited to those of the above arrangement, so another arrangement cannaturally be used. Furthermore, although isochronous transfer is used inthis embodiment, the above arrangement is applicable to another transfersystem such as bulk transfer.

[0133] The automatic interface switching will be described next.

[0134] As described in the first embodiment, the 1394 driver 31 monitorsthe connection of the 1394 by detecting the power supply voltage of apower supply twisted pair line of 1394 twisted pair lines, and outputsthe connection state to the MPU 23. The USB driver 47 also monitors theconnection of the USB from the signal statuses of USB twisted pair linesand outputs the connection state to the MPU 23.

[0135] First, connection switching when the 1394 driver 31 is the masterwill be described. In this case, 1394 connection is performed as much aspossible. The 1394 driver 31 applies a control signal from the 1394 busand the 1394 connection state data described earlier to the MPU 23.While the 1394 driver 31 is applying to the MPU 23 the data indicatingthat the 1394 bus is connected, the MPU 23 holds the 1394 driver 31active in order to set the communication mode in the 1394 mode. Also,upon receiving this 1394 setting signal, the MPU 23 holds the USB driver47 in sleep.

[0136] When the 1394 driver 31 is disconnected from the 1394 bus, thepower supply voltage of the power supply twisted pair line of the 1394twisted pair lines drops, The 1394 driver 31 detects this voltage dropand outputs to the MPU 23 data indicating that the 1394 driver 31 isdisconnected from the 1394 bus. When receiving this data, the MPU 23sets the 1394 driver 31 in sleep and the USB driver 47 active.

[0137] Next, connection switching when the USB driver 47 is the masterwill be described. In this case, USB connection is performed as much aspossible. The USB driver 47 applies a control signal from the USB busand the USB connection state data described previously to the MPU 23.The USB bus signal operates as differential signals. The differentialsignals are D+ and D−. When the USB driver 47 is connected to the USBbus, one of the D+ and D− holds a voltage higher than a maximum valueVSE(MAX) of a single-end threshold, and the other has a voltage lowerthan VSE(MAX). The USB driver 47 detects this state and applies dataindicating USB bus connection to the MPU 23. While the USB driver 47 isinputting, to the MPU 23, the data indicating that the USB bus isconnected, the MPU 23 holds the USB driver 47 active in order to set thecommunication mode in the USB mode. Also, upon receiving this USBsetting signal, the MPU 23 holds the 1394 driver 31 in sleep.

[0138] When the USB driver 47 is disconnected from the USB bus, thevoltages of both D+ and D− become lower than the voltage VSE(MAX). Ifthis state continues for 2.5 μsec or longer, the USB driver 47determines that the connection is cut. The USB driver 47 outputs, to theMPU 23, data indicating that the USB driver 47 is disconnected from theUSB bus. Upon receiving this data, the MPU 23 sets the communicationmode in the 1394 mode. Also, the MPU 23 sets the USB driver 47 in sleepand the 1394 driver 31 active.

[0139] The switching performed to set the 1394 or the USB as the mastercan also be performed by the user by using a switch (not shown) or thelike. Also, the 1394 can be set as the master by a standard operation,and this can be reset when the power supply is turned on. Alternatively,the USB can be set as the master by a standard operation, and this canbe reset when the power supply is turned on. Any arbitrary setting canbe performed as long as the apparatus operates as above.

[0140] The above embodiments have been described by using two digitalI/Fs. However, the present invention similarly applicable to anapparatus including three or more digital I/Fs such as the IEEE1394, theUSB, and RS-232C.

[0141] In other words, the foregoing description of embodiments has beengiven for illustrative purposes only and not to be constructed asimposing any limitation in every respect.

[0142] The scope of the invention is, therefore, to be determined solelyby the following claims and not limited by the text of thespecifications and alterations made within the scope equivalent to thescope of the claims fall within the true spirit and scope of theinvention.

What is claimed is:
 1. A communication method of transmitting andreceiving command data for controlling a device connected to acommunication line by selecting an arbitrary one of a plurality ofdifferent communication systems, wherein at least some of a plurality ofcommand data of each of said different communication systems are used inall of said communication systems.
 2. A method according to claim 1,wherein said different communication systems include a communicationsystem based on an IEEE1394 standard.
 3. A method according to claim 1,wherein said different communication systems include a communicationsystem based on an RS-232C standard.
 4. A method according to claim 1,wherein said different communication systems include a communicationsystem based on an RS-422 standard.
 5. A method according to claim 1,wherein said different communication systems include a communicationsystem based on a USB standard.
 6. A communication method oftransmitting and receiving command data for controlling a deviceconnected to a communication line by selecting an arbitrary one of aplurality of different communication systems and, on the basis of thereceived command data, generating control data for a device connected tosaid communication line, wherein at least some of a plurality of commanddata generated by each of said different communication systems are usedin all of said communication systems.
 7. A method according to claim 6,wherein said different communication systems include a communicationsystem based on an IEEE1394 standard.
 8. A method according to claim 6,wherein said different communication systems include a communicationsystem based on an RS-232C standard.
 9. A method according to claim 6,wherein said different communication systems include a communicationsystem based on an RS-422 standard.
 10. A method according to claim 6,wherein said different communication systems include a communicationsystem based on a USB standard.
 11. A communication apparatuscomprising: a) a plurality of communicating means provided in aone-to-one correspondence with a plurality of different communicationsystems to transmit and receive command data for controlling a deviceconnected to a communication line; and b) decoding means for decodingthe command data received by said plurality of communicating means andcontrolling a device connected to said communication line, wherein saiddecoding means generates common control data for command data receivedby said plurality of communicating means by respective communicationsystems thereof and having the same function.
 12. An apparatus accordingto claim 11, wherein said decoding means comprises storage means forstoring, in advance, the control data for controlling a device connectedto said communication line, and address generating means for generatingan address in said storage means storing the control data, in accordancewith the command data received by said plurality of communicating means,and said address generating means generates the same address in saidstorage means for the command data received by said plurality ofcommunicating means by respective communication systems thereof andhaving the same function.
 13. An apparatus according to claim 11,wherein the command data received by said plurality of communicatingmeans by respective communication systems thereof and having the samefunction use the same code data.
 14. An apparatus according to claim 11,wherein said plurality of communicating means include communicatingmeans based on an IEEE1394 standard.
 15. An apparatus according to claim14, wherein said plurality of communicating means include communicatingmeans based on an RS-232C standard.
 16. An apparatus according to claim14, wherein said plurality of communicating means include communicatingmeans based on an RS-422 standard.
 17. An apparatus according to claim14, wherein said plurality of communicating means include communicatingmeans based on a USB standard.
 18. A communication apparatus comprising: a) a plurality of communicating means provided in a one-to-onecorrespondence with a plurality of different communication systems totransmit and receive command data for controlling a device connected toa communication line; and b) supply means for supplying the command datato said plurality of communicating means, wherein at least some of aplurality of command data, supplied by said supply means, of each ofsaid different communication systems are used in all of saidcommunication systems.
 19. An apparatus according to claim 18, whereinsaid plurality of communicating means include communicating means basedon an IEEE1394 standard.
 20. An apparatus according to claim 19, whereinsaid plurality of communicating means include communicating means basedon an RS-232C standard.
 21. An apparatus according to claim 19, whereinsaid plurality of communicating means include communicating means basedon an RS-422 standard.
 22. An apparatus according to claim 19, whereinsaid plurality of communicating means include communicating means basedon a USB standard.
 23. A communication apparatus comp rising: a) aplurality of communicating means provided in a one-to-one correspondencewith a plurality of different communication systems to transmit andreceive command data for controlling a device connected to acommunication line; and b) decoding means for decoding the command datareceived by said plurality of communicating means and controlling adevice connected to said communication line, wherein said plurality ofcommunicating means comprise at least first communicating means capableof transmitting and receiving N command data and second communicatingmeans capable of transmitting and receiving M command data, and at leastsome of the M command data are included in the N command data.
 24. Anapparatus according to claim 23, wherein said plurality of communicatingmeans include communicating means based on an IEEE1394 standard.
 25. Anapparatus according to claim 24, wherein said plurality of communicatingmeans include communicating means based on an RS-232C standard.
 26. Anapparatus according to claim 24, wherein said plurality of communicatingmeans include communicating means based on an RS-422 standard.
 27. Anapparatus according to claim 24, wherein said plurality of communicatingmeans include communicating means based on a USB standard.
 28. Acommunication apparatus comprising: a) first communicating means forperforming data communication in accordance with a first communicationsystem; b) second communicating means for performing data communicationin accordance with a second communication system different from saidfirst communication system; c) first detecting means for detecting aconnection state of said first communicating means with respect to acommunication line; and d) control means for controlling switchingbetween said first and second communicating means in accordance with anoutput from said first detecting means.
 29. An apparatus according toclaim 28, wherein said first communicating means comprises power supplymeans for supplying power.
 30. An apparatus according to claim 29,wherein said first detecting means detects the connection state of saidfirst communicating means by measuring a power supply voltage of saidpower supply means.
 31. An apparatus according to claim 30, wherein saidfirst detecting means measures the power supply voltage of said powersupply means at predetermined time intervals and detects the connectionstate of said first communicating means in accordance with themeasurement result.
 32. An apparatus according to claim 28, wherein saidplurality of communicating means include communicating means based on anIEEE1394 standard.
 33. An apparatus according to claim 32, wherein saidplurality of communicating means include communicating means based on anRS-232C standard.
 34. An apparatus according to claim 32, wherein saidplurality of communicating means include communicating means based on anRS-422 standard.
 35. An apparatus according to claim 32, wherein saidplurality of communicating means include communicating means based on aUSB standard.
 36. An apparatus according to claim 32, wherein saidsecond communicating means performs a differential operation.
 37. Anapparatus according to claim 28, further comprising: second detectingmeans for detecting a connection state of said second communicatingmeans with respect to a communication line, wherein said control meanscontrols switching between said first and second communicating means inaccordance with an output from said first detecting means or an outputfrom said second detecting means.
 38. An apparatus according to claim37, wherein said second communicating means comprises power supply meansfor supplying power.
 39. An apparatus according to claim 38, whereinsaid second detecting means detects the connection state of said secondcommunicating means by measuring a power supply voltage of said powersupply means.
 40. An apparatus according to claim 39, wherein saidsecond detecting means measures the power supply voltage of said powersupply means at predetermined time intervals and detects the connectionstate of said second communicating means in accordance with themeasurement result.
 41. An apparatus according to claim 37, wherein saidsecond detecting means detects the connection state of said secondcommunicating means in accordance with a voltage level on a signal lineof a communication line.
 42. A communication method comprising: a firstcommunication mode which performs data communication on a firstcommunication line on the basis of a first communication system, and asecond mode which performs data communication on a second communicationline on the basis of a second communication system different from saidfirst communication system, wherein said communication modes areswitched in accordance with a connection state with respect to saidfirst communication line for said first communication system.